Although for all intents and purposes, they aren’t protected by the US Constitution either.
Ever since the Civil Rights Act, Americans have not been permitted to decide who they rent their property to, who they do business with and who they will enter into contracts with.
My husband and I are likely the only two people in Canada who believe that a property owner should have the right to decide who can and cannot make use of his property, even for arbitrary or offensive reasons. And are willing to say so publicly. Your mileage may vary.
Although I don’t think “teenage unwed mother” is “arbitrary”. It’s called a sane, commonsensical assessment of risk and reward. And she should have planned her life a little better (like both my teenage unwed mother half-sisters, who I wouldn’t have rented apartments to either — until they married the guys, which they at least managed to do, albeit briefly…)
Those Woolworth’s lunch counter guys have a LOT to answer for…